Abstract

<p>Spectral Library: The Berlin Emissivity
Database (BED) is a spectral library containing the
emissivity measurements of several planetary
analogues. It contains currently entries for
plagioclase and potassium feldspars, low Ca and
high Ca pyroxenes, olivines, elemental sulphur,
common martian analogues (JSC Mars-1, Salten
Skov, palagonites, montmorillonite, hematite,
goethite) and a lunar highland soil sample measured
in the wavelength range from 3 to 50 µm as a
function of particle size. For each sample, the
spectra of four well defined particle size separates
(&lt;25 µm , 25-63 µm, 63-125 µm, 125-250 µm) are
measured with a 4 cm-1 spectral resolution. These
size separates have been selected as typical
representations for most of the planetary surfaces
[1].</p><p>Laboratory set-up: The instrumentation is
located in the Planetary Emissivity Laboratory
(PEL) at the Institute for Planetary Research (PF) of
the German Aerospace Center (DLR) in Berlin,
Germany. It consists of a spectrometer attached to
an external emissivity device. The Bruker VERTEX
80v spectrometer, has a very high spectral resolution
(better then 0.2 cm-1), and a resolving power of
better than 300,000:1, and can be operated under
vacuum conditions. To cover the entire 1 to 50 µm
spectral range, two detectors, a liquid nitrogen
cooled MTC and a room temperature DTGS and
two beamsplitter, a KBr and a Multilayer are used to
measure the same target.</p><p>
The emissivity device is composed of the sample
chamber, a double-walled box with three apertures:
a 15 cm squared door used to insert the cup in the
box, a 5 cm rounded opening through which the
beam is directed to the spectrometer and a 5 cm
opening facing the attached blackbody unit. A
heater is placed in the chamber and is used to heat
the cup with samples from the bottom. The thermal
radiation emitted normal to the surface by the
sample or the blackbody is collected by an Aucoated
parabolic off-axis mirror and reflected to the
entrance port of the spectrometer. Figure 1 shows
the emissivity device attached to the spectrometer
external port: the sample chamber is opened to show
the parabolic mirror mounted on a mechanical arm
and oriented toward the reference blackbody, the
sample heater and the purging system.</p><p>
A pump circulates water at a constant
temperature in the volume between the inner and
outer walls of the chamber. The surfaces of the box
are painted with black high emissivity paint. The
chamber is purged with dry air to remove
particulates, water vapour and CO<sub>2</sub>. Further details
can be found in [2, 3].</p><p>
Emissivity spectra: In Figure 2 an example of
quartz measurements for two extreme grain sizes is
shown, together with analogue measurements
extracted from the ASU and ASTER spectral
libraries. Complementary to the existing datasets
(ASU and ASTER), the BED library sensibly extend
both the investigated spectral range and the grain
size ranges. The enormous difference between the
spectra of the small and large fractions witness the
need for such a complete dataset for a correct
interpretation of remote sensing data.</p><p>
Martian analogues: The emission spectra of
standard martian analogue materials like the JSC
Mars-1 (a palagonitic tephra from Hawaii, USA),
the Salten Skov (a Fe-oxide precipitate from the
Midjutland region of Denmark), montmorillonite,
hematite, goethite and some palagonites from
Hawaii, USA, are shown and discussed in this
paper.</p><p>
References: [1] Helbert, J. et al. (2007), ASR 40,
DOI:10.1016/j.asr.2006.11.004. [2] Maturilli, A. et al.
(2006), PSS 54. [3] Maturilli, A. et al. (2007), in press
on PSS.</p>